The present invention relates to a motor controller.
To control the speed and torque of a synchronous motor, it is necessary to detect or infer the pole position. By executing current control or voltage control on the basis of the detected pole position, the speed and torque of a synchronous motor can be controlled.
In recent years, a pole position sensorless control system for controlling a synchronous motor without detecting the pole position of the synchronous motor by a position sensor has been proposed.
For example, the first control method described in Japanese Application Patent Laid-Open Publication No. Hei 07-245981 and Electric Society, Industry Application Department, National Convention No. 170 in the 8th years of Heisei is a method for applying an alternating voltage and inferring the pole position on the basis of the parallel component and orthogonal component (current component in the rotatory coordinate system) of the motor current for the voltage and the position of the magnetic pole can be detected without using a pole position sensor during stopping or at a low speed.
Further, the second method for superimposing an additional voltage described in Japanese Application Patent Laid-Open Publication No. Hei 11-150983 and Japanese Application Patent Laid-Open Publication No. Hei 11-69884 is a method for realizing no-use of a pole position sensor within the range from low load to high load during stopping or at a low speed by adding an applied voltage so as to prevent magnetic saturation even in the high torque region.
Further, the third control method described in Japanese Application Patent Laid-Open Publication No. Hei 08-205578 is a method for detecting the saliency of a synchronous motor from the mutual relation between the vector of a voltage applied to the synchronous motor by the pulse width control (PWM control) and the ripple component (current difference vector) of the motor current for it. The third method uses a general PWM signal for controlling the voltage of the synchronous motor, so that there is an advantage that there is no need to load an additional signal for detection.
Further, the voltage vector means a voltage having the magnitude and direction decided from a three-phase voltage or d-axis and q-axis voltages. The same may be said with the current vector and hereinafter, each phase voltage as an element or the d-axis and q-axis voltages and the voltage vector as a sum total will be explained appropriately. Further, for the synchronous motor, the pole position of the rotor is to be detected, so that the pole position will be explained hereunder. For a reluctance motor, the specific position of a rotor having saliency is detected.
Further, a control method for detecting the pole position of a rotor in the same way as with the aforementioned method on the basis of the difference in inductance between the q axis and the q axis using the magnetic saturation characteristic of an induction motor is proposed.
Therefore, when the aforementioned is to be described together, the pole position and the specific position of the reluctance motor will be referred to as a rotor position.
In the first control method mentioned above, to detect the pole position by driving the motor, it is necessary to extract a current having the same frequency component as that of the detection alternating voltage by a band pass filter such as a notch filter and Fourier integration. Particularly, when the number of revolutions of the motor is increased, the separation between the input frequency of the motor and the frequency of the detection alternating voltage is difficult and a problem arises in that stable driving control at high speed rotation is difficult. Further, it is necessary to consider so as to prevent effect by the switching characteristic of the invertor. Namely, the carrier-frequency of the PWM signal is several kHz to 20 kHz, while the frequency of the detection alternating voltage is low such as several hundreds Hz, so that during driving control for the motor, noise of several hundreds Hz may be generated.
Further, the second control method mentioned above is intended to improve the characteristics for drive-controlling the motor in a stop state or a low-speed rotation state, and the relation between the current detection timing which is important for drive-controlling the motor at high-speed rotation and the PWM signal is not taken into account, and highly accurate position detection is not taken into account.
Further, the third control method mentioned above requires, to realize it, to detect the mutual relation between the condition of the motor current and the applied voltage every changing of the PWM signal. Namely, for one period of the carrier, it is necessary to detect the motor current condition at least 6 times and confirm the applied voltage condition, so that a problem arises that a highly precise controller must be used.
An object of the present invention is to propose an inexpensive and highly precise motor controller.
Another object of the present invention is to propose a motor controller for controlling an AC motor with high precision by suppressing an increase in motor loss within the wide range from stop state to high-speed rotation state using one current detector.
Still another object of the present invention is to propose a motor controller for detecting the rotor position of an AC motor without applying a detection voltage to the AC motor.
The present invention has an AC motor, a power converter for applying a voltage to the AC motor by a PWM signal generated by comparing a command value with a carrier, and a controller for detecting the rotor position of the AC motor and controlling the command value and is characterized in that the position of the rotor is detected on the basis of the difference between the real current differential vector and the reference current differential vector.